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Since the first report on the ability of nuchal translucency measurement to detect pregnancies affected by Down's syndrome by Nicolaides et al in 19941 over 20studies have been published on the issue. Despite all these efforts, however, the exact performance of nuchal translucency measurement in detecting Down's syndrome is still unknown. Recent large studies in low risk populations have evaluated the performance of nuchal translucency measurement in detecting Down's syndrome, but the result of the nuchal translucency measurement had already been used in the risk assessment (by identifying cases of Down's syndrome that would never have reached term). In these studies fetuses affected by Down's syndrome which have an increased nuchal translucency are thus more likely to be detected than those affected fetuses with a normal nuchal translucency‐and this may inflate the reported detection rate of nuchal translucency measurement.2^–4 Even the two largest studies reported detection rates as different as 72%5 and 54%.6 As a consequence, the choice between nuchal translucency measurement and serum screening for Down's syndrome remains subject to debate. 78

The paper by Hyett et al in …